Thermal switch



Jan. 25, 1944. H. M. ACLY zrm. 2,340,099

THERMAL SWITCH I Filed Jan. 4. 1943 Inventors: Harry M. A-cly, JamesR. Bar-1", b WW5. (9

y The'lrAt-borney Patented Jan. 25, 1944 I Harry'M. Acly and James R. Barr, Pittsfleld,

Mass., assignors to General Electric Company, a corporation of New York Application January 4, 1943, Serial No. areas 6 Claims. (01. 200-138) element in a predetermined position until it is pulled away with a snap action upon distortion of the thermal element thereby to move the contact arm to one position with a snap action, together with a latch which holds the strip in this position while the thermal element returns to its former shape and moves nearer the magnet. Fi nally, the thermal element ispulled by the magnet with a snap action back to its first position, and during its final snap element moves the latch to disengagethe flexible contact arm which thereupon snaps to its other circuit position in accordance with its bias.

For a more complete understanding of our in vention, reference should he had to the accompanying drawing, Fig. l of which is an elevation view partly in section of a thermal switch embodying our invention taken along the line i-\1 of Fig. 2 looking in the direction of the arrows and showing the switch in a normal position; Fig. 2 is a plan view of the'devlceshown in Fig. 1; while Fig. 3 is a fragmentary view showing the switch latched in its other position.

Referring to the drawing, in one iorrn of our invention we provide a thermal element in the form of a straight bimetallic strip it ends. mov able switch arm or member in the form of a spring strip i i, these strips having their leit hand ends, as seen in Fig. l, suitably secured as by screws respectively to lined projections it and it secured to the casing or support it. The two strips are thus secured in substantially parallel relation with each other.

On its free end the spring strip li'carries on one side a movable contact it arranged to engage a cooperating stationary contact to secured to the support it, and on its other side a movable contact its normally in engagement as shown with a stationary contact it! secured to the support it. The strip it is preformed and mounted on the projection is so as to bias its free end by its ownspring force shown in the drawing, with the movablecontact to a normal position, as

movement, the thermal tilt lfia in closed circuit engagement with the stationary'oontact 5%.

A snap action is given the movable end of the thermostatic strip ill by means of a permanent magnet ll secured to the support just below the strip it near its movable end, an armature i8 made of magnetic material being carried by the strip Ill in position to be attracted to the magnet H, as shown in the drawing. This magnet, as shown, is a cylindrical block or disc which is suitably secured to the base it as by embedding it partially in the molded electrically insulating material of which the base i4 is formed. On its upper surface forming a pole face, the magnet is provided with a diametric groove is separating its north and south poles.

The armature it is suitably secured to the bimetallic strip it, as by welding. Preferably also, the armature is provided on its surface adjacent the pole faces of the magnet with a layer till made of a suitable nonmagnetic material, such as copper, for the purposeof providing an air gap to assure a uniform pull on the armature when the armature is in its attracted position. This air gap is preferably about .003 inch thick.

The magnet ill preferably is made of a material having a high magnetic retentivity, such as a mixture of aluminum, nickel, copper and iron, as described and claimed in U. S. Patent No. 1,947,- 27%, issued on February 13, 1934 to William E. Ruder and in U. S. Patent No. 2,027,994, issued on January it, 1936 to Tokushichi Mishima.

We have also provided a spring latch ill secured to a projection 22 on the base and extending downward, as seen in Fig: 1, at right angles with the two strips and passing through an aperture 235 in the strip it. with a latching projection it which, when the strip it is bent upward into engagement with the contact this on the lower side of the strip ii and is moved toward the left hand by the spring force of the strip M to a position below the left-hand wall of the opening 23 whereby the strip ii is held in this position as shown in Fi 3.

as shown in Fig. l of the drawing, however,

the spring latch 2 l is bent toward the right hand by the rlght=hand end of the bimetal strip it which engagesthe lower end of the latch. The hirnetal strip it in this position is pulled downward by the magnet, the armature it being in its attracted position. To effect this releasin movement of the latch toward the right hand, the lower end of thedatch and the end of the thermostat it, or a member carried by the ther- This latch is provided mostat, are shaped to give a camming action. Thus, as shown, the lower end 25 of the latch is bent into a curved form toward the left hand while the end oi the birnetal strip I is provided with a cooperating bent end 20. Thus when the bimetal strip is pulled downward by the armature, its end 28 engaging the curved portion 25 oi the latch forces the latch toward the right hand to a position, as shown in the drawing, in which the latching projection 24 with the strip ll.

In the opertaion 01' the device it will be as,- sumed that an increase in temperature causes the thermal strip I 0 to fiex in such a manner that its right-hand end tends to move upward. This end, however, is at first held by the magnet until the distorting force 01' the thermal strip becomes strong enough to pull forcibly the armature away from the magnet whereupon the thermal strip moves quickly to its distorted shape. During this snap movement the righthand end of the thermal strip moves upward and a button 21 carried by it, made of electrically insulating material. engages the spring strip H adjacent its right-hand end bending the strip upward and moving its right-hand end upward quickly thereby to disengage the contact Ila from the contact lBb and bring the contact II into engagement with the stationary contact II, as shown in Fig. 3. At this time the latch 2|, having been released at its lower end by the upward movement of the termal strip. springs toward the left hand so that its latching projection 24 latches the spring switch arm in this circuit position.

To effect the reverse movement of the switch arm II, the end of the thermal strip ll must move downward and. assuming that this downward movement is efiected by cooling or the strip, as the strip cool. its right-hand end moves gradually downward bringing the armature ll nearer and nearer the magnet. Finally as the armature approaches the magnet, the pull on it exerted by the magnet becomes great enough to overcome the stiffness or strength of the thermal strip and bend the thermal strip. The armature is then snapped quickly to its attracted position thereby moving the right-hand end of the thermal strip downward quickly and causing it to engage and move quickly the latch 2| toward the right-hand thereby releasing the switch arm H which immediately moves in accordance with its bias to its normal circuit position. It is contemplated that the cooperating engaging portions and 2| of the latch and the thermal strip II will be shaped and positioned so that they engage only after the snap movement of the portion 20 beins in its downward direction. Thus the latch is snapped quickly to its fully unlatched position thereby positively unlatching the switch arm.

It will be understood that the switch arm II can be connected to operate any suitable switching means. Also, one or the two pairs 01' contacts, the normally open contacts II, I or the normally closed contacts Ila, llb, can be omitted if desired so that the switching means will be either normally closed or normally open.

While we have shown a particular embodiment of our invention, it will be understood. or course,

that we do not wish to be limited therein since many modifications may be made. and we therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

is moved out of engagement What we claim as new and desire to secure by Letters Patent oi. the United States is:

1. A thermal switch comprising a movably mounted switch member, means biasing said switch member to a first predetermined circuit position, a thermally responsive operating device movable from one position to another position in response to a predetermined change in temperature thereby to move said switch member against its bias to another circuit position, means for causing said operating device to move with a snap action in each direction between its said positions,.. and a latch for holding said switch member in said other circuit position engaged and moved by said operating device to a position to release said switch member when said operating device snaps back to said one position, said latch being structurally independent of said operating device and in spaced relation with said operating said switch member device when said operating device is in said other position.

2. A thermal switch comprising a stationary contact, a movably mounted'switch member carrying a movable contact cooperating with said stationary contact, means biasing said switch member to a first circuit position, a thermally respons ve operating device movable from one position to another position in response to a predetermined change in temperature thereby to move said switch member to a second circuit position, means for causing said operating'device to move with a snap action in each direction between said positions thereby to operate said switch members with a snap action to said second' circuit position, and a latch for holding said switch member in said second' circuit position. said latch being structurally independent of said operating device thereby to provide for movement of said operating device independently of said latch during the initial return movement or said operating device but engaged and moved by said operating device to a position to release said switch member when said operating device snaps back to said one position.

'3. A thermal switch comprising a stationary contact, a movably mounted switch member carrying a movable contact, means biasing said switch-member to a first circuit position in which said movable contact is in a predetermined relation with said stationary contact, a latch for said switch member arranged to engage and hold said switch member in a' second circuit position when said switch member is moved to that position, a thermally responsive operating device for moving to said second circuit p0sition in response to a predetermined temperature, means cooperating with said operating device tor causing said operating device to move; with a snap action Just before it engages said switch member thereby to move said switch member with a snap action to said second circuit position to be held by said latch; said snap means operating device to return with a snap action after it has disengaged said switch as aooe switch arm in a second circuit position against its bias to said first circuit position, a thermally responsive operating device, an armature moved by said operating device, a magnet tor normally biasing said armature to an attracted position, cooperating means on said latch and said operating device engaging when said armature is moved by said magnet to its attractedposition thereby to move said latch to a position to release said switch arm, and means carried by said operating device for engaging and moving said switch arm to its second circuit position with a snap action when said operating device pulls said armature away from said magnet in response to a change in temperature.

5. A thermal switch comprising a stationary contact, a spring switch arm having one end secured and carrying a movable contact on its other end, said strip being preformed andsecured at its fixed end so that it holds normally by its own resiliency said movable contact in a predetermined first circuit relation with said stationary contact,'a spring latch for engaging said switch arm thereby to hold said switch arm in a second circuit position, a bimetallic strip, an armature carried by said bimetallic strip adjacent its free end, a magnet for normally biasing said armature to an attracted position, cooperating means on said latch and said bimetallic strip engaging when said armature is in its attracted position thereby to movesaid latch to a position to release said switch arm, and means carried by said bimetallic strip for engaging and moving said switch arm to said second circuit position with a snap action when said bimetallic strip pulls said armature away from said magnet in response to a change in temperature.

6. A thermal switch comprising a switch member mounted for movement between first and second positions, means biasing said switch member to said first position, a thermally responsive operating device movable from one position to another in response to a predetermined change in temperature, means for causing said operating device to move with a snap action in each direction between its said positions, means on said operating device in normal spaced relation with said switch member for engaging said switch member after said operating device has started its snap movement in moving to one of its positions whereby said switch member is moved quickly against its bias to its said second position, a latch member biased to engage and hold said switch member in said second position, and means on said latch engaged by said operating device after said operating device has started its snap movement in moving back to the other of its positions whereby said latch is moved quickly to release said switch member for movement to its said first position in accordance with its bias.

' HARRY M. ACLY.

JAMES R. BARR. 

